The utilization of an automatic lift apparatus in connection with railroad cars, trucks, and other similar vehicles to aid in loading and unloading is well known in the art. Such an apparatus is often essential when a loading dock is unavailable or inconvenient. Further, use of such an apparatus increases productivity by permitting easier handling of bulky, unwieldy, palletized or other heavy loads. The apparatus must be strong in order to achieve a large load lifting capacity. However, the apparatus must not weigh so much that it significantly decreases the load carrying capacity of the vehicle. Therefore, there are competing design concerns for such an apparatus. The apparatus load capacity must be tempered by the weight that the apparatus adds to the vehicle. Other design factors the apparatus' convenience of use and durability.
One type of lift apparatus is the hydraulic self-storing style. These lifts are often capable of moving to a stored position under the bed of the vehicle. Such lifts typically employ a pair of hydraulically powered parallelogram linkages to support the lift platform. These lifts, however, are dependent upon rear axle location due to their mounting requirements. The lifts are typically also constructed of heavy steel to withstand the torsional forces exerted by the load when lifting the lift platform. These forces also require the platforms to be loaded evenly to avoid binding. Further, since the lift platform usually passes through the linkages about a pivotal connection when storing, the platforms often rattle in their stored positions. As the vehicle passes over uneven surfaces, this rattling exerts considerable force on the pivotal connections. This style of lift does have the advantage, though, in that they are stored under the bed of the vehicle, thereby allowing the vehicle to directly back up to a loading dock. Other styles of lifts, including rail lifts, require the additional step of moving the lift apparatus into a loading dock position from its storage position before backing up to a loading dock.
Rail lift systems solve many of the problems experienced by the hydraulic self-storing style lifts. Rail lifts are typically lighter in weight, have a more evenly distributed lift, and are less prone to bouncing and rattling when in their stored positions. Typically, these lifts utilize a platform supported at the platform's edge closest to the vehicle by the lower portion of elevator members connected to opposing vertical rails. Support members at the platform's edge furthest away from the vehicle are attached to the upper portion of the elevator members. In this manner, rail lifts raise the platform from each of the platform's four corners, thereby providing a more uniform lift.
To store rail lift style platforms, typically the platform is moved from a horizontal to a vertical position against the rear of the vehicle. In this position the lift hinders the loading and unloading of the vehicle. Further, since the lift is often not required when a loading dock is present, these lifts require that the operator of the vehicle move the lift to a "loading dock" position prior to backing up to a loading dock. This loading dock position usually encompasses moving the platform from a vertical position against the rear of the vehicle, to a vertical position directly beneath its original stored position but below the horizontal plane formed by the bed of the vehicle. This position typically decreases the vehicle's ground clearance. Therefore, these types of lifts often encounter problems if the ground close to the loading dock is uneven. Further, the operator of the vehicle is typically unable to back up completely to the dock without potentially damaging the rail lift.
A rail lift designed by Collins (U.S. Pat. No. 4,627,784) attempted to solve several of these problems associated with rail lifts in connection with side doors of railroad cars. The Collins rail lift utilizes a "swing-away" lift apparatus. In this device, the lift rails and platform swing as a unit to a position parallel and slightly beneath the plane formed by the railroad car bed. The whole assembly is pushed under the bed of the railroad car to be stored when not in use. The device is located on the side of the railroad car at the car's approximate midpoint, thereby fitting between the railroad car axles. However, this device is not practical for a rear loading vehicle since there is limited room beneath the rear end of most vehicles due to axle placement. This is especially the case in many trucks. Further, this lift is very complicated in its operation and storage.
Therefore, there exists a need to develop a rail lift which is stored in a position beneath the rear portion of a vehicle bed while not limiting ground clearance, disturbing axle placement, or requiring an additional transfer step when a loading dock is available.